Change plan to 3 days per week

Depends on distance and how long your plan is.
Some plans have this possibility, but you have to check on your own which.

Thanks Adam. It’s for a marathon, doesn’t look like I have the option to change it unfortunately. I also don’t seem to be able to move the sessions between different days which is a shame. 

I assume you use adaptive plan, don't bother to move your session to other day, in adaptive plans it doesn't make sense because each workout is adjusted to your current shape.